I am really dumb so I can explain the basics of midi in an easy way for you i think. Yes it is very confusing.
Basically what the MIDI is doing... ummmmmmmmm..... let me start out with what it isn't doing...................
MIDI isn't like pluggin a microphone into your recorder, and you sing into it, and the computer hears it. This type of signal (the voice) is an "acoustic signal." Like wise an electric guitar coming out of an amplifier, or the sound coming out of keyboard speakers. All "acoustic signal." Kind of makes it easy in my mind to just think of that type of sound source as "analog."
OK. What MIDI does (what you are tryin' to get it to do (it can do more then just this, but let's keep this as simple as possible....))
MIDI doesn't make a sound. OK your Alexis SR 16 is a keyboard or drum machine right? Some kind of electronic instrument......
First of all. What you are tryin' to do sounds like what is called using Alexis as a "MIDI controller."
You could just think of it as a "controller." Like on xbox. It's just like that. You use the controller to tell Super Mario what to do in the game.
When you use a controller in music production programs........
well first you would have your VIRTUAL instrument up in ACID right? If it's a sample, or a plugin.... what I mean by a plugin would be for example another program..... BUT it's like a virtual piano (or anything) it's a virtual instrument that is designed to sit inside of your ACID, and play sounds that you tell it how to play.
Your virtual instrument.... it can be a sampler... or it can be something that plays some music that you wrote in the program.... or..... it can be controlled externally by a MIDI controller like your Alexis....
This has a big advantage sometimes for writing music, or performing live with DAW and pluggins.
As you can use the virtual instruments sound library, or a sample library that you may own, and control the composition or performance in real time with your keyboard or external sequencer. It's good for recording your ideas as well and having more control over your sound.
To set up is a bit of a challenge, and learning curve can be hard, but it's not to bad. Not knowing ACID... I assume there must be some type of way the user can configure the MIDI controller settings.
That is basics of how you get it to work. You find how to set up the programs settings for MIDI controllers, and assign it all properly, and make sure you have the driver for your MIDI to USB devices.
hope this helps a little....